When Joseph Hill turned 21, he went from being homeless to being homeless and uninsured.

Hill grew up in foster care. He entered the system when he was 3 months old, and lived in 10 different foster homes in San Diego. At 19, he aged out of foster care and faced an abrupt transition into adulthood.

At first he received health insurance under Medi-Cal, California's version of Medicaid. But those benefits disappeared when he turned 21.

Back then, Hill needed new prescription glasses so he could drive to work and see the board at school. Losing medical coverage meant spending money that he did not have.

"It felt like a low blow — it cost like $400," Hill says of paying out of pocket for his glasses. "If I had coverage, I could have put that $400 to groceries."

But now, because of a little-known provision in the Affordable Care Act, Hill and other former foster youth can get free health care under Medicaid until age 26, regardless of their income. In some states, coverage includes free vision and dental care. The new provision mirrors a similar Medicaid expansion granted to young adults on their parents' insurance.

About 55,000 former foster youth are expected to take advantage of the Medicaid expansion this year, and that number is predicted to increase by 2017 to as many as 74,000, according to the Centers for Medicare and Medicaid Services.

Brooks is an advocate for the expanded coverage, but she says the change does not come without hiccups.

Although state governments must cover youth who age out of the foster care system in their own states, Brooks says state governments are not required to extend coverage to former foster youth who aged out in a different state.

The change also comes with challenges. Finding and notifying eligible members of this notoriously hard-to-reach demographic is the biggest, says Fatima Morales of Children Now, a California-based children's health advocacy group. Her organization's new campaign, Coveredtil26, aims to inform California's estimated 27,000 former foster youth, like Hill, about their new health care eligibility and ease their transition into adulthood.

Hill, who is now 23 and covered under Medi-Cal, felt the provision's effects firsthand during a recent trip to the eyeglass store.

"I got a free pair and a backup in case they break," he says. "And I didn't have to pay a cent."